We are interested in understanding the patterning system that diversifies morphology on the anterior-posterior axis of animal embryos, and how changes in this system drive morphological evolution. The homeotic (Hox) genes, important in the development of normal human form, are key factors in this patterning system, but other homeotic modulator proteins act in parallel and downstream to adjust and realize Hox morphological output. Some of the parallel modulators work by regulating Hox transcriptional activation and repression functions. How does evolution in Hox system components regulate morphological diversity? We will take advantage of the diversity in arthropod appendage number to define molecular changes in homologous Hox proteins and/or Hox-regulated enhancers that control appendage morphological evolution in different taxa. In particular, we will focus on mechanisms underlying the different regulatory effects of orthologous insect and crustacean Hox proteins on appendage-promoting genes. Candidate mechanisms in Hox proteins and Hox modulatory factors that may vary in evolution include DNA binding functions, or transcriptional activation/repression functions. How do do paralogous Hox proteins diversify morphology in different Drosophila segments? We will study whether the head Hox Deformed protein and other Hox proteins directly regulate cell death promoting realizator genes such as reaper. We will also test how Distal-less transcription is differentially regulated in head segments by Deformed and Deformed modulator proteins such as Cap 'n' collar B. Microarray methods will be used to test whether the battery of genes regulated by Deformed is similar to the battery of genes regulated by thoracic and abdominal Hox proteins. Is there a common regulatory code that specifies skeletal development in most animals? We will define and analyze a head skeleton-specific enhancer at the Drosophila Dopa decarboxylase locus. We will test whether this enhancer is regulated by Hox, Spen, Tsh, and Drosophila homologs of mammalian skeletal transcription factors. We will apply microarrays to test whether this combination of transcription factors regulates a common group of "skeletal" and/or "collagen and cross-linking" genes in Drosophila and other animals.